Polymers of alpha-olefins prepared in the presence of ionic catalyst systems, for example, polypropylene prepared using a catalyst comprised of diethylaluminum chloride and a titanium trichloride, contain greater or lesser amounts of low molecular weight, and particularly, amorphous components which, when taken alone, are alkane soluble materials. The presence of these alkane-soluble materials in the polymers leads to difficulties during the fabrication of products therefrom and to inferior physical properties in the finished items, and hence are almost always removed in commercial processes for the production of polypropylene. Also, production of these components leads to economic disabilities for the process as they have little usefulness and extra process steps are generally required to remove them from the commercial product and, in the slurry process, from the polymerization medium prior to recycle of the medium.
In the past a number of materials and combinations thereof have been reported in the patent literature as useful modifiers for transition metal compound-alkylaluminum component alpha-olefin catalysts to reduce the alkane-soluble fraction produced during the polymerization process. Among these modifiers are amines, amine oxides, ethers, organophosphites, combinations of organotin sulfides and amines, amine oxides or organophosphites, and combinations of hydrogen sulfide with amines, amine oxides, organophosphites or ethers. The combinations containing organotin sulfides or hydrogen sulfide have been described as showing a greater effect on solubles reduction while exerting little adverse effect on yield than either component of the combination alone. However, such mixtures have some disadvantages which include the cost of organotin sulfides, the presence of traces of tin in the polymer, the formation of line clogging precipitates when hydrogen sulfide and certain aluminum alkyl compounds are combined, and the toxicity of hydrogen sulfide.
Since it is generally true that slowing an alpha-olefin polymerization down produces more of the crystalline polymer, and that modifiers when their concentrations become high enough decrease the polymerization rate, the object of the work leading to the invention described herein is to obtain maximum solubles reduction with the smallest adverse effect upon yield while maintaining the commercially important properties of the product polymer. Even small changes in solubles and yield can have large economic effects when the amount of polymer produced per year is extremely large.
Further, in vapor phase or bulk polymerization it is convenient to add the modifiers and aluminum alkyl component dissolved in inert medium into the reactor in a separate stream from the one containing the titanium compound. If the modifiers and alkylaluminum compound form a precipitate, line clogging in the stream can be a problem and it has been observed that the two catalysts streams are combined improperly in the reactor resulting in deteriorated product properties.
Now it has been found that by using sulfur dioxide and certain amines together as a modifier, catalyst compositions are formed which when used for propylene polymerization result in a substantial reduction of the alkane soluble fraction without serious decrease in polymer yield. Such compositions can show better solubles reduction than shown by either additive when used alone. In addition, the compositions taught herein can result in improvements in certain polymer properties when used in the convenient split addition mode in vapor state and bulk polymerization process. In addition, in slurry polymerization processes wherein a slurry of the polymeric product is commonly washed with an aqueous medium, the use of compositions containing bis-(2-ethoxyethyl) amine as disclosed herein is particularly advantageous in that bis-(2-ethoxyethyl) amine is highly soluble in water and therefore aqueous washing of the polymer slurry will serve to substantially remove this amine from the slurry thereby reducing levels of the amine in not only the final polymeric product but also, in the polymerization medium such that recycle of the same is facilitated.
The catalyst systems disclosed herein can be used for alpha-olefin polymerization wherein supported or other types of high activity titanium compound catalyst components are employed to make highly crystalline product.